With the emergence of new technologies for mobile telephony, packet-based communication solutions using Internet Protocol (IP) have been developed to support the usage of multimedia services, while different mobile and fixed user terminals with new functionalities for multimedia communication are emerging on the market. Services are also constantly being developed for terminal users to increase the field of usage and enhance the experience when generally consuming communication services.
An IP Multimedia Subsystem (IMS) network can be used for enabling multimedia services and other communication services by initiating and controlling sessions for user terminals connected to various different access networks. The sessions are handled by specific session control nodes in the IMS network, including those referred to as Call Session Control Function (CSCF) nodes.
The signaling protocol Session Initiation Protocol (SIP) is used for multimedia sessions in IMS networks and other communication services networks.
Various identities may be associated with IMS, such as private user identities, IP Multimedia Private Identity (IMPI) and public user identities, IP Multimedia Public Identity (IMPU). Both IMPI and IMPU are Uniform Resource Identifiers (URIs) that can be digits (a Tel URI, like tel:+1-555-123-4567) or alphanumeric identifiers (a SIP URI, like sip:john.doe@example.com). IMS identities are stored in a subscriber database, hereinafter referred to as a Home Subscriber Server (HSS) together with subscriber service profiles, service triggers and other information.
The IMPI is a unique permanently allocated global identity assigned by the home network operator, and is used, for example, for Registration, Authorization, Administration, and Accounting purposes. Every IMS user shall have one or more IMPI.
The IMPU is used by any user for requesting communications with other users. The IMPU can be published (e.g. in phone books, web pages, business cards). There can be multiple IMPU per IMPI. The IMPU can also be shared between several terminals, so that several terminals can be reached with the same identity (for example, a single phone-number for an entire family).
IMPUs may be stored in the HSS as Wildcarded Public User Identities (wIMPUs). The wIMPU represents a collection of IMPUs that share the same service profile and are included in the same Implicit Registration Set (IRS). An IRS is a group of IMPUs that are registered via a single registration request. When one of the IMPUs within the set is registered, all IMPUs associated with the IRS are registered at the same time. wIMPUs include a regular expression (reg exp) that defines the identities that should be matched and handled as defined for the wIMPU.
A Public Service Identity (PSI) identifies a service, or a specific resource created for a service on an Application Server (AS). The PSI is stored in the HSS either as a distinct PSI or as a wildcarded PSI. The distinct PSI contains the PSI that is used in routing, whilst the wildcarded PSI represents a collection of PSIs. The format of the wPSI is the same as for the wIMPU.
The handling of wildcarded identities, i.e. wPSIs and wIMPUs, was specified in the Third Generation Project Partnership (3GPP) Release 7 and 8 respectively, see for instance 3rd Generation Partnership Project (3GPP) TS 23.003. wIMPU has been included in the standards to support Private Branch Exchanges (PBX) where thousands of numbers can be registered from one single identity. Implicit registration is not applicable as downloading thousands of implicit identities registered to the rest of the system is not an option (the message would be too long).
There has therefore been a need for the wIMPU which is associated with a group of IMPUs sharing the same service profile and requiring a single explicit registration to provide services to all the identities behind a PBX. The following conditions are applicable for the wIPMU:                The subscription under a wIMPU will be handled by the same Serving CSCF (S-CSCF) in the situation of routing towards the core or by the same PBX in the situation of routing in the interface (Gm) between a user terminal, hereinafter called a User Equipment (UE), and the IMS network, so that no further checking is needed.        No individual authentication of the IMPUs within a wIPMU is performed.        No individual service profile is provisioned anywhere in the network for the distinct IMPUs within a wIMPU.        There is no interface (Ut) between UEs and Applications Servers (AS) available for individual IMPUs included within a wIMPU as they will all have only one authentication information.        There is no individual service setting provisioned anywhere in the network for the distinct IMPUs within a wIMPU. Standards state that an AS can only store service data on the wIMPU, that is, only one set of transparent data for the whole wIMPU.        All the users within the number range of a wIMPU should belong to the same IRS, therefore they need to belong to the same subscription.        All the wIMPUs and the distinct IMPUs within the wIMPU from one subscription should be provisioned in the same HSS.        
There are thus certain limitations in terms of services and profiles applicable for the distinct IMPUs within the range of a wIMPU. In specific cases it might therefore be desired to assign a different service profile for a distinct IMPU within a wIMPU. As an example, the president of a company, even though having a phone number from the same range as the rest of the company, could be assigned a different service profile. Consequently the different service profile assigned to the president would be provisioned in the HSS as a distinct IMPU. It could also be desired that the president could use his mobile UE to receive calls to/from his company's phone number. However, this may result in undesired forking of terminating calls. The above described desired special treatment of distinct identities within a wildcarded identity is not completely supported in the present standards. There is therefore a need for solutions that provide better support for such situations.